In a couple of earlier posts, I mentioned the use of PVRTC compressed images for OpenGL texture mapping. I don't know if this is new, or if I just failed to see them earlier, but Apple now has a technote on the format along with some sample code. These are both part of the iPhone Dev Center, so you'll need to be a member of the iPhone Dev program (free version okay) to access them.
Also, if you attended WWDC last year, the attendee site is still available so you can still download presentation materials. The Touch Fighter sample code from the session 703 is a great resource for wrapping your head around OpenGL (you can also get a copy of that if you go to one of the iPhone Tech Talks) If you have access to the WWDC video library, the video and presentations for sessions 708 and 703 are good OpenGL resources also.